The British Rail Class 313 is a dual-voltage EMU train built by British Rail Engineering Limited's Holgate Road carriage works between February 1976 and April 1977.

They were the first production units that were derived from British Rail's 1971 prototype suburban EMU design which, as the BREL 1972 family, eventually encompassed 755 vehicles over five production classes (313, 314, 315, 507 and 508). They were the first second-generation EMUs to be constructed for British Rail and the first British Rail units with both a pantograph for 25 kV 50 Hz AC overhead lines and contact shoe equipment for 750 V DC third rail supply. They were, additionally, the first units in Britain to employ multi-function automatic Tightlock couplers, which include electrical and pneumatic connections allowing the coupling and uncoupling of units to be performed unassisted by the driver whilst in the cab.

The Class 313 units were the oldest EMUs operating on the National Rail network in Great Britain prior to their withdrawal in 2023, having entered service in 1976. However, the even older 1972 Stock and 1973 Stock are still in service on London Underground.

Network Rail leased Beacon Rail-owned unit 313121 as a test vehicle for the ERTMS installation on the Hertford Loop. The unit was repainted into Network Rail's yellow house colours and internally refurbished at Alstom's Wembley Intercity Depot, to include a new driving desk, technician's workstation, kitchen and toilet facilities, and the necessary ERTMS equipment.

It was expected to be used again when ERTMS was ready for testing on the Great Western Main Line, but Network Rail instead listed the unit for sale by tender in January 2023. The Railway Heritage Designation Advisory Board had originally designated unit 313201 for potential preservation after retirement, on the grounds that it was the first Class 313 unit built, and by extension the first production PEP-derived unit. However, in early 2023, the board decided instead to designate Network Rail's unit 313121, as unlike 313201 it retains its original seating and dual-voltage running equipment.